Filled polymers are a special grade of composites that represent unique application promises in chemical sensing element, functional extrusion films, gas separation membranes, solvent-free coatings and maskants, and light-weight composites with high thermo-oxidative stability [J. Lou, “Filled polymers”, in Encyclopedia of Chemical Processing, S. Lee, ed., Marcel Dekker, New York, N.Y., 2004].
One particular area most relevant to chemical engineers is the gas separation membranes [R. W. Baker and J. G. Wijmans, “Membrane separation of organic vapors from gas streams,” in Polymeric Gas Separation Membranes, D. R. Paul and Y. P. Yampolskii, eds., CRC Press, Boca Raton, Fla., 1994]. Significant changes in free volumes are expected of non-crystalline polymers by incorporating selected filler particles whose dimensions enable them to interfere with the packing of the polymer chains. It is possible that nanofillers will influence the packing density of glassy and rubbery polymers thus change the permeability of the polymer and at the same time change the selectivity if such influences are gas-specific. Elastomeric silicones of chosen molecular weight are among the polymers that we feel have a great likelihood to be modified by fillers to create high performance perm-selective membranes by adjusting the loading and binding details of filler particles in the polymer matrix. Such flexible filled polymer composites are expected to have much different permeabilities compared with conventional membranes without nanofiller interference. When the size of the fillers is at the molecular level the nature of the filler impact changes. This is an exciting area, not only promising in applications but also bearing potential for significant theoretical breakthroughs.